The searchlight signal is generally a single lamp device located along the wayside of a railroad to provide information to the locomotive concerning current track operating conditions. The searchlight signals are generally a single lamp device in which the color of the signal light source is colored either red, green, or yellow by interposing colored lens in front of the single lamp. The devices are normally designed with the yellow and green lenses being held away from the light path by gravity and/or springs such that the device tends to fail in the red mode. The locomotive engineer interprets the red signal as a warning and normally would proceed to stop forward motion on such a track. The green signal is generally an all clear signal, and generally indicates no safety speed restrictions on that block of track. The yellow is a caution and its specific operating requirements may vary with different railways, but is usually indicated to proceed at some limited speed of operation of the train into the next section of track. It can be understood that a false energization or a sticking of the lens in the yellow or green positions could result in an error condition in which the vital mode of operation on the section of track would not be properly communicated to the on-board personnel. It is therefore highly desirable that in any failure mode the red signal be shown.
One way in which the lens systems have been operated is through the use of a bipolar or double acting electric solenoid. Typically when the electric solenoid is activated by a current of a given polarity it will move the yellow lens in front of the light source, and when the solenoid is activated by a current of the reverse polarity the green lens will be moved into the path of the light source. With the solenoid deenergized the green and yellow lenses are withdrawn from the path of the light source and the red lens is positioned to give a red signal. At any time in which the operation of the signal light is in doubt it is desirable to show the most restrictive color, namely red, or no light signal whatsoever. If the light signal is not given, the locomotive engineer can then assume that the signal is not functioning properly and take appropriate action, such as would be usually done under the red or most restrictive condition. Mechanically interlocking the red, green, and yellow lenses helps to assure the correct operation of a given signal. Such signal lights have always been a concern in the railway industry, and it has been a practice to better indicate the correct signal by having switches mounted on each color lens, especially the yellow and green lenses. These switches are activated when the respective lens is either fully engaged or fully removed from the light source path. Prior art solutions to insure reliability and vitality of operation have been to run the contacts from the respective yellow and green lens switches down from the light mast via a cableway to the wayside control where such contacts have been used in a relaying system to check and verify the position of the respect yellow and green lenses. Such verification could then indicate whether a malfunction had occurred and appropriate circuitry at the wayside could provide for a back-up operating condition. Under such back-up position the circuitry would generally prevent lamp energization unless the proper lens carrier was in the proper position. The wiring arrangement generally used in the prior circuits would be eight wires going back to the wayside control from the signal, namely one pair from the yellow contacts, one pair from the green contacts, one pair from the light filament, and one pair for the bipolar solenoid operation. Such additional wiring, cabling, and the associated inter-connections can introduce other potential failure problems such as conductor to conductor shorts within the cable bundles.
It is one of the objects of this invention to provide for vital operation of a multi-color searchlight while limiting the number of wires that must be run between the wayside signal control and the signal light device itself. In addition to achieving a vital searchlight operation, the circuits also reduce the number of conductors that must be run thereby improving the ease of installation and reducing the chances for large multiple conductors to cause the circuit to have shorts or cross connections.
It is also one of the objects of this invention to provide for a direct and simple circuit that can be checked for vitality and that is compatible with existing searchlight mechanisms.